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Did Penn & Teller tell a lie? On the biased nature of spinning coins. (English) Zbl 1360.62072

From the text: We were featured on television as experts to confirm one of the “true” assertions that when spun, pennies land tails up 80% of the time. To demonstrate this phenomenon, we performed an “experiment” appearing to have spun 30,000 new pennies and recorded approximately 80% of the spins as tails. We hope it is clear to the reader that this “experiment” relied heavily on the magic of television. (Note that at 15 seconds per spin, it would take over 5 days to spin all 30.000 pennies). […] There were two claims about spinning pennies made during the episode in which we had little confidence:
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Pennies will land tails-up approximately 80% of the time.
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This bias is due to extra weight added on the heads side of the coin, or according to Penn Jillette, “Lincoln’s fat head.”
Therefore, as academics, the only reasonable solution seemed to be to dig out some pennies, read some physics, and attempt to determine the truth behind these claims.

MSC:

62F03 Parametric hypothesis testing
70E18 Motion of a rigid body in contact with a solid surface
70B10 Kinematics of a rigid body
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